Unify window presentation and frame-driven shell motion

Share window geometry across overview, resize snapshots and retained closes. Advance close handoffs and group retained rendering by stacking position.

Drive shell motion from surface frames, reuse settled widget content, and synchronize notification materials with each card's fade. Replace physical config keys with duration and bounce, and update documentation and regression coverage.

compositor/src/state.rs

@@ -160,7 +160,8 @@ impl FocusSwipe {
         let distance = self.destination - self.start;
         // When both columns already fit, give bounded drag feedback and settle
         // back to the unchanged viewport after selecting the next window.
-        let distance = if distance.abs() < 0.001 {
+
+        if distance.abs() < 0.001 {
             if self.direction == Direction::Right {
                 64.0
             } else {
@@ -168,8 +169,7 @@ impl FocusSwipe {
             }
         } else {
             distance
-        };
-        distance
+        }
     }
 
     fn position(&self) -> f64 {
@@ -266,8 +266,12 @@ impl WorkspaceSlide {
     }
 
     fn position(&self, item: &WorkspaceSlideItem, delta: Duration) -> SlideOffset {
+        self.sample(item, delta).0
+    }
+
+    fn sample(&self, item: &WorkspaceSlideItem, delta: Duration) -> (SlideOffset, SlideOffset) {
         if let Some(progress) = self.held_progress {
-            return item.start.between(item.target, progress);
+            return (item.start.between(item.target, progress), item.velocity);
         }
         let mut x = AnimatedValue {
             current: item.start.x,
@@ -281,10 +285,16 @@ impl WorkspaceSlide {
         };
         x.advance(delta, self.spring);
         y.advance(delta, self.spring);
-        SlideOffset {
-            x: x.current,
-            y: y.current,
-        }
+        (
+            SlideOffset {
+                x: x.current,
+                y: y.current,
+            },
+            SlideOffset {
+                x: x.velocity,
+                y: y.velocity,
+            },
+        )
     }
 
     fn moving(&self) -> bool {
@@ -1105,6 +1115,27 @@ impl ClientData for ClientState {
 
 #[cfg(test)]
 mod tests {
+    #[test]
+    fn slide_item_sampling_matches_advance_without_mutating_the_slide() {
+        let mut slide = WorkspaceSlide::new(None, WorkspaceId(1), WorkspaceId(2), SwipeDirection::Up);
+        slide.advance(Duration::from_millis(30));
+        for held in [None, Some(0.35)] {
+            slide.held_progress = held;
+            for delta in [Duration::ZERO, Duration::from_millis(8), Duration::from_millis(400)] {
+                let before = (slide.items[0].start, slide.items[0].velocity);
+                let mut reference = slide.clone();
+                reference.advance(delta);
+                for (item, advanced) in slide.items.iter().zip(&reference.items) {
+                    let (position, velocity) = slide.sample(item, delta);
+                    let expected = held.map_or(advanced.start, |p| advanced.start.between(advanced.target, p));
+                    assert_eq!(position, expected);
+                    assert_eq!(velocity, advanced.velocity);
+                }
+                assert_eq!((slide.items[0].start, slide.items[0].velocity), before);
+            }
+        }
+    }
+
     #[test]
     fn workspace_reversal_keeps_position_and_velocity() {
         let from = WorkspaceId(1);